Many piston blanks are currently forged in a manner that creates a heavy forged blank with a top-heavy flange. Such conventional piston blanks require substantial machining to cut away material to create a flange or collar over a recess such that the collar can then be bent to form a closed cooling channel. Methods for forming cooling channels in single-piece pistons are disclosed in U.S. Pat. Nos. 6,763,757 and 7,918,022, both of which are herein incorporated by reference in their entireties.
It would be desirable to forge a piston blank closer to the shape of a final piston, herein called a “near-net” shape. Conventionally, forging a piston blank to a near-net shape was considered difficult for a number of reasons. Forging involves high temperatures and brute force. Thus, it is somewhat counterintuitive that forging could lead to a predictable piston shape with predictable and repeatable dimensions as would be desired for a near-net shape piston blank. Additionally, forging near-net shape piston blanks with existing equipment presents substantial challenges to those of ordinary skill in the art.
Forging methods have been developed that may provide manufacturing and/or cost and efficiency advantages.